1. Field of the Invention
The present invention relates to digital video and, more particularly, to a method for estimating a motion vector for transcoding digital video.
2. Description of the Related Art
Video standards and display resolution of terminals receiving video and networks for transmitting video vary, need for transcoding digital video is gradually increasing.
Transcoding is a technique of converting, for example, the format or the size of a video stream for reproduction at different terminals. A first type of transcoding converts a bit stream coded in one video standard into a different video standard. A second type of transcoding converts resolution of video to be compatiable with a display of a receiving terminal. A third type of transcoding converts transmission bit rate of video so as to be suitable for a bandwidth of a network for transmitting the video.
Referring to FIG. 1, a conventional video transcoder includes a decoder 10 for decoding an input bit stream, a signal processor 20 for processing a signal to transcode a signal outputted from the decoder 10, and a coder 30 for estimating and encoding a motion vector of a signal outputted from the signal processor 20. An optimum motion vector is set through motion estimation. Estimation of a motion vector in the video coding is a very complex process as well as in transcoding.
According to conventional video decoding, a transcoder receives from an inputted bit stream that is a compressed video stream. The transcoder selects a base motion vector (BMV) from motion vectors obtained from the inputted bit stream. For estimation of motion vectors, a search region is set around the base motion vector. The search region has a window width approximately two pixels surrounding the base motion vector.
A search is performed within the search region to obtain a sum-and-difference (SAD) between the base motion vector and each pixel of the search region. The motion vector is estimated by using the full search method. A motion vector of a pixel is selected that has the smallest SAD among the calculated SADs. The base motion vector and the motion vector of a pixel with the smallest SAD are summed to create an estimated motion vector. The calculation complexity is increased depending on the number of pixels calculated in the search region. In this example, 25 calculations are required to calculate the SADs associated with 25 pixels.
Therefore, there is a need for improved system and method for estimating motional vectors that overcomes the above problems and provides advantages over conventional coding systems.